Among cameras capable of being connected to a USB, some cameras can control timing of image data reading from a recording medium (memory card) or timing of image data writing on a USB bus in accordance with a transfer mode (isochronous transfer/bulk transfer) at the time of USB connection (Japanese Patent Application Laid-Open No. 10-136245). In a case of a first transfer mode that assures a certain transfer rate (isochronous transfer mode), such camera parallelly performs image data reading of one frame from a CCD or a recording medium to store in a memory (RAM) and image data reading of one frame from a memory (RAM) to output on a USB bus. In a case of a second transfer mode that does not assure a certain transfer rate (bulk transfer mode), image data writing of one frame is performed after image data reading of one frame is completed. By virtue of this configuration, image data can be transferred for sure in any of the first and second transfer modes. Furthermore, the camera has a function for informing a connected host of a desired transfer method (isochronous transfer/bulk transfer). By virtue of this function, data transfer can be performed in the most appropriate transfer mode in accordance with the size of image data subjected to streaming playback.
Moreover, there is a control apparatus that performs control in accordance with a USB speed mode (High speed/Full speed) (Japanese Patent Application Laid-Open No. 2003-150539). This control apparatus comprises display means for displaying which of the first speed mode (High speed) or the second speed mode (Full speed) is set at the time of connection. Note that a detailed description regarding a USB is found in, e.g., “Universal Serial Bus Specification Revision 2.0, Apr. 27, 2000.”
However in the conventional art, in a case where the foregoing camera transfers image data in an encoding format according to, e.g., Moving Picture Experts Group (MPEG) where decoding timing is defined on a playback side, decoding processing may not be performed in time on the playback side, and buffer underflow can occur. Furthermore, since image data transfer depends upon image data reading processing, in a case where data is transferred in a format where audio data and image data are multiplexed, the image data and the audio data may lose synchronism on the playback side and proper reproduction may not be realized.
Furthermore, in a case where the aforementioned control apparatus has a data transfer function that can secure a bandwidth only for high-speed connection, in other words, a function that cannot realize data transfer in full-speed connection due to lack of bandwidth, there is a problem in that a user is unable to know intuitively whether or not the function can be realized based on the speed mode at the time of USB connection.